1. Field of the Invention
The present invention relates generally to a viscous fluid coupling device. In particular, the present invention is concerned with a floating wiper mounted on a pump plate of a viscous fluid fan clutch.
2. Statement of the Related Art
A thermostatically-controlled viscous fluid clutch assembly for driving and rotating a vehicle cooling fan is well-known. A multi-bladed fan is removably secured to a body of the clutch assembly. The fan and clutch assembly are installed between an accessory pulley of a vehicle engine (typically the water pump pulley) and a radiator. The clutch assembly drives the fan at high speeds close to input speed when cooling is required and permits the fan to rotate at low speeds when cooling is not required. Thermostatic control of the fan through the clutch assembly reduces the load on an engine and the noise caused by fan rotation, resulting in horsepower gain and improved fuel economy.
Generally, a clutch assembly includes a clutch plate having lands and grooves mated to the body having complementary lands and grooves. A pump plate separates a pair of internally-contained chambers, a collecting chamber and a pumping chamber, from a reservoir. Gates in the pump plate permit the flow of a viscous fluid from the reservoir to the collecting chamber and into a shear zone between the lands and grooves of the body and clutch plate. Fluid sheared between the lands and grooves transfers input torque from the clutch plate to drive the body and the attached fan.
Fluid flow through the pump plate gates is controlled by a control arm placed adjacent the pump plate. When cooling is not required, the control arm is rotated so that the gates are covered and the majority of the fluid in the shear zone is pumped into the pumping chamber. Orifices in the pump plate permit passage of the fluid from the pumping chamber into the reservoir. The removal of a majority of the fluid from the shear zone substantially reduces the shear between the clutch plate and the body, thereby substantially reducing the rotation of the fan.
When cooling is required, the control arm is rotated an opposite direction to uncover the gates and permit fluid to flow into the shear zone, thereby increasing the shearing force between the clutch plate and the body. This increase in input torque results in faster rotation of the fan to increase the flow of cooling air.
Oftentimes, a bimetallic element is utilized to actuate the control arm, and thus the flow of fluid through the pump plate gates. The bimetallic element may be connected to a control shaft which is in turn connected to the control arm. As the bimetallic element expands due to the temperature of warm ambient air, the shaft rotates, thereby causing the rotation of the control arm. As the ambient air cools, the bimetallic element contracts, causing the control shaft and the control arm to rotate in an opposite direction.
It is well-known to provide wiper elements on a surface of the pump plate in communication with the pumping chamber. A plurality of wipers project from the pump plate adjacent each pump plate orifice into the pumping chamber. Each wiper can be formed as a thin, flat element secured to the pump plate usually by welding. In other embodiments, a wiper may be integrally formed with the pump plate by stamping a projection in a pump plate adjacent each pump plate orifice. As a fan clutch is rotated, an increase in fluid pressure in the pumping chamber occurs as the wiper creates a fluid dam. The increase in fluid pressure results in increased fluid flow through the pump plate orifices.
Control of machining and assembly tolerances are important to the function of conventional fluid clutch assemblies. A particular area where tolerances must be closely checked and controlled involves the wiper and the pumping chamber. During formation of a pump plate, the height of a stamped or welded wiper must be closely controlled. To maximize the pump-out efficiency of a clutch assembly, it is desirable that the wiper extend as far as possible into the pumping chamber. Of course, the height of a manufactured wiper cannot exceed the allotted design height. Furthermore, the distance between the pump plate and the clutch plate must be controlled so as to provide adequate space for receiving the wipers. The height of wipers and the width of pumping chambers are usually in the range of a few thousandths of an inch. Control of these dimensions adds to the costs of machining and assembly. In order to reduce costs, conventional clutch designs shorten the height of wipers to provide extra space and accommodate machining and assembly variances.
The art continues to seek improvements. It is desirable to provide wipers in a pumping chamber to enhance the pump-out of the chamber. Concurrently, it is desirable to provide a clutch design wherein the machining and assembly costs can be reduced.